Question : The mean of 20 observations was 42. It was found later that observation 54 was wrongly taken as 45. The corrected new mean is:
Option 1: 45.42
Option 2: 43.5
Option 3: 44.25
Option 4: 42.45
Correct Answer: 42.45
Solution :
The mean of 20 initial observations = 42
Sum of initial observations = 42 × 20 = 840
Wrong entry = 45
Correct entry = 54
Sum after correction = 840 – 45 + 54 = 849
$\therefore$ Final mean = $\frac{849}{20}$ = 42.45
Hence, the correct answer is 42.45.
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